Veined cutting tools as described in U.S. Pat. Nos. 4,713,286 and 4,762,445 provide for drills, end mills, reamers and other cutting tools with multiple cutting edges fixed to a tungsten carbide body using a sintered abrasive particulate such as diamond (PCD) or CBN. These tools have proven to be advantageous in drilling, reaming, and milling various advanced composite materials and non-ferrous materials and are now well known as cutting tools.
Generally, the high cost and delicate nature of these tools restrict them to use only where cutting conditions can be closely controlled by computer numerically controlled (CNC) machines to avoid impact, vibrations, and/or variable feed conditions that would destroy the cutting edges.
One area where such veined PCD or PCBN tools are widely used is in drilling advanced carbon fiber reinforced plastic (CFRP) composites and stackups of these materials with aluminum or titanium on CNC equipment for advanced aircraft frames. However, many areas of these planes do not allow for the use of CNC drilling equipment making portable power feed air motors the preferred method of drilling the necessary fastener holes.
Prior to this invention, the use of PCD or PCBN drills with these air motors was not considered feasible for drilling difficult materials like layers of advanced composites and titanium. Typically, these air motors use what is called a hard tooling fixture with guide bushings. PCD or PCBN drills were known to chip the sides or margins of the drill as they were guided by these bushings due to the delicate nature of the exposed PCD cutting edge.
U.S. Pat. No. 5,611,251 also teaches a method of making a PCD or PCBN drill using a brazeable PCD or PCBN blank and makes reference to other variations for brazeable PCD and PCBN drill construction using commercially available blanks from Megadiamond or Debeers.
Such cutting tool construction taught or referenced by U.S. Pat. No. 5,611,251 invariably uses low rake angles to strengthen the cutting edge and to compensate for the ready nature of these edges that tend to chip. Such art does not teach a way of preventing the chipping of the cutting edges.
In view of the limitations of prior art PCD drill bits, reamers, and milling cutting tools, the present invention was developed to address these limitations and is an improved PCD cutting tool having a shielded PCD or PCBN cutting edge.